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From Alasdair Nottingham <>
Subject Re: jpa blueprint ns handler question
Date Mon, 08 Nov 2010 17:27:06 GMT

Alasdair Nottingham

On 8 Nov 2010, at 17:02, Jarek Gawor <> wrote:

> On Fri, Nov 5, 2010 at 5:05 PM, Alasdair Nottingham <> wrote:
>> Alasdair
>> On 5 Nov 2010, at 20:16, Jarek Gawor <> wrote:
>>> On Fri, Nov 5, 2010 at 6:08 AM, Timothy Ward <>
>>>> To clarify, the aim when designing this function was to make consuming persistence
units and contexts as simple as possible - hence trying to make sure that it could be expressed
as a single element.
>>>> The primary injection mechanism people use is by setters, which in blueprint
would be something like:
>>>> <property name="foo" ref="bar"/>
>>>> In order to get JPA to be similarly concise, and to avoid breaking the existing
validation requirements of Blueprint, we came up with the <unit/> and <context/>
tags, which contain the information from an @PersistenceContext and @PersistenceUnit annotation.
>>>> The decision was made that:
>>>> <property name="emf" type="javax.persistence.EntityManagerFactory">
>>>>   <jpa:unit unitname="myUnit"/>
>>>> </property>
>>>> was significantly less usable than:
>>>> <jpa:unit property="emf" unitname="myUnit"/>
>>> I disagree. To me the following is much clearer:
>>> <property name="emf">
>>>  <jpa:unit unitname="myUnit">
>>> </property>
>>> And this syntax is consistent with rest of the blueprint syntax, i.e.
>>> how you would inject a bean as a property or argument. The <jpa:unit/>
>>> and <jpa:context/> provide a specific object just like a <bean/>
>>> <reference/>, etc. and should be handled in the same way, IMHO.
>> It depends on what you consider jpa:context is doing. I you think it defines a bean
that is an entity manager then I understand your point, if you consider it the equivalent
of @PersistenceContext then I think the scheme as is makes sense.
> I'm not really sure what you mean by that. The current ns handler
> either injects a <reference/> (for EntityManagerFactory) or a <bean/>
> (for EntityManager)...
> I think we should also consider that this is Blueprint injection. It
> has different rules than Java EE, e.g. it supports array or list
> injection, etc. We should ensure that our solutions take advantage of
> these differences. We shouldn't limit ourselves to what is possible or
> not in Java EE.

I was specifically referring to your comment about one form making more sense than another.
I was pointing out that which is simpler or clearer and depends on what you think jpa:context
means. I was not commenting on the relative validity of the two XML snippets.

> Jarek

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